1. Field of the Invention
This invention relates to a block assembly having a weighing means incorporated therein, and particularly to such an assembly having compression load measuring means.
2. Description of the Prior Art
Block assemblies incorporating weighing means have generally used two types of weighing means or load cells. These assemblies have used either compression-type load cells or extension-type load cells. Weigh block assemblies using extension-type load cells generally comprise connecting the load directly to one end of the load cell while supporting the other end of the load cell in the support housing which may be attached to, for example, a sheave basket. Among the disadvantages of this arrangement are the possibility of the complete failure of the block as a load-carrying device upon failure of the load cell if adequate safety restraints are not included. If the load exceeds the load rating of the load cell and the extension load cell fails, it is possible that the entire block assembly may fail and the load connected to the lower end of the load cell may be dropped.
The weigh block assemblies incorporating compression-type load cells generally mount the compression load cell between an upper member attached to the load-carrying element and a lower member secured to the housing, so that the compression-type load cell is compressed between the members as the weigh block assembly is loaded. This arrangement reduces the possibility of load failure upon failure of the load cell. If the load cell fails, the loading member may engage the supporting member to avoid dropping the load from the assembly.
Examples of weigh block assemblies incorporating compression-type load cells are shown in the following U.S. Pat. Nos. 2,820,624 issued to Koegel; 3,080,935 issued to Abbonizio et al.; 3,081,833 issued to Kester; and 3,095,057 issued to Kraeling.
In the past, these weigh block assemblies using compression type load cells have included means to prevent lateral or side loading on the load cells. For example, in the patent issued to Kester, a pair of flat leaf springs are provided on each side of the upper member to prevent lateral movement of the upper member. Other weigh block assemblies have used flexure plates or check rods to stabilize the upper member and to reduce or eliminate side-loading effects on the upper member. These lateral restraints have had an adverse effect on the accuracy of the load cells in measuring the weight of the load attached to the block. The flexure plates or check rods were designed with the intent of absorbing all side loads without absorbing an excessive amount of vertical load, but in practice, the lateral restraints did absorb a certain portion of the vertical load, resulting in inaccurate measurements. In addition, absorption of the vertical load in a nonlinear or nonrepeatable fashion would add to the unreliability of the system since the sensed weight would become erratic and unpredictable. In addition, many times the flexure plates or check rods become loose due to vibrations and shocks experienced by the assembly causing a change in the original predicted value of the load being absorbed.